1. Field of the Invention
The present invention relates to apparatus allowing partial reads of storage locations containing data that may change between sequential reads. For instance, for a storage location storing a double word, the system of the present invention allows byte, word, or double word accessing of the storage location.
2. Description of Related Art
Typical data processing systems include a host processor and one or more peripheral devices. Often, the peripheral devices maintain information for use by the host in a memory which is updated independent of the host. The storage locations containing the information may include a plurality of bytes per host address. The host may have a need to read one or more bytes from the storage location without reading all of the bytes at a single time. Also, the host may be limited to reading a subset of the plurality of bytes at a time by access paths involved.
When the storage location contains dynamically changing data, such as counters, and the like, there is the potential that a partial read of one section of the storage location followed by a partial read of the other section would yield useless results because of changes to the information that occur between the reads. For instance, the host could erroneously read 01ff (hex) as it reads a four byte register a byte at a time, while the actual contents of the register increment from 00ff to 0100. Thus, it is desirable to provide a mechanism that allows section wide reads of a multi-section register containing dynamic data.